How does the narrator of Garth Stein's novel The Art of Racing in the Rain describe the soul?

Early in
's novel , the story's narrator, the aging canine Enzo, discusses the basis
for his belief that he will be reincarnated as a human being. That belief, inspired by a
television show he has seen, involves the concept of a human soul inside a dog's body:

"Sure, Im stuffed into a dogs body, but thats just the shell.
Its whats inside thats important. The soul. And my soul is very human."

With this observation, Enzo continues to reflect on the importance
of his soul and the role it plays in his plan to convince his human owner, Denny, to have him
put to sleep so that transformative process towards becoming human can commence. Enzo can't
explain the concept of a soul any better than most humans, noting that it is "a thing that
has no surface, no sides, no pages, no form of any kind," but which exists nonetheless.
Enzo proceeds to put forth a scientifically and spiritually-derived (and, he...